Obesity: glypican-4: role in insulin signalling

Modulation of GPC-4 and GPLD1 serum levels by improving glycemic indices in type 2 diabetes: Resistance training and hawthorn extract intervention

Aims

This study was designed to investigate the effects of resistance training (RT) and hawthorn extract (Ha) on Glypican-4 (GPC-4) and Insulin-regulated glycosylphosphatidylinositol-specific phospholipase D (GPLD1) serum levels in T2DM and to examine the relationship of these variables with glycemic indexes.

Method

40 male Wistar rats were divided into five equal groups: Healthy Control (H-C), Diabetes Control (D-C), Diabetes Resistance training (D-RT), Diabetes Hawthorn (D-Ha), and Diabetes Resistance training Hawthorn (D-RT-Ha). T2DM was induced with a 4-week high-fat diet (HFD) and one dose of STZ intraperitoneal injection (35 mg/kg). 1-week after the injection, RT (with a range of 50%-100%1RM/3 day/week) and gavage of Ha extract (100 mg/kg/day) was performed for 12 weeks.

Results

The glycemic indices improvement (reducing blood glucose and increasing serum insulin level) caused by RT and/or Ha increased GPC-4 and decreased GPLD1 in the T2DM rats, but these positive changes were more effective in the combination of RT + Ha. A strong correlation was also observed between GPC-4 and GPLD1 with blood glucose and insulin.

Conclusion

The increase in serum GPC-4 levels was probably due to the direct effect of RT + Ha, and the improvement of glycemic indexes after RT and Ha. The double effect of RT + Ha can be a regulatory mechanism for GPC-4 and its related factors in controlling T2DM complications.

The response of serum Glypican-4 levels and its potential regulatory mechanism to endurance training and chamomile flowers' hydroethanolic extract in streptozotocin-nicotinamide-induced diabetic rats

AIMS

Glypican-4 (GPC-4) is a novel adipomyokine that enhances insulin signaling. Glycosylphosphatidylinositol-specific phospholipase D (GPLD1) is thought to release GPC-4 and is itself an insulin-regulated enzyme. Beneficial effects of exercise training and chamomile flowers extract (CFE) are shown through activation of PPARγ, which is a promising drug target in diabetes and associated with GPC-4 synthesis. This study investigated the effects of 14-week treadmill running and CFE on serum GPC-4, GPLD1, and insulin levels in streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats.

METHODS

Thirty-two STZ-NA-induced diabetic male Wistar rats were randomly assigned to four groups: control (C), training (T), CFE treatment (CFE), and training plus CFE treatment (TCFE) groups. The training groups were exercised on treadmill 5 days/week and the treating groups were fed with 200 mg/kg/day CFE in drinking water for 14 weeks. Finally, serum GPC-4, GPLD1, and insulin levels were analyzed via sandwich ELISA.

RESULTS

Compared to the control group, serum insulin levels were significantly higher in the T, CFE, and TCFE groups (p < 0.05, p < 0.05, p < 0.01, respectively), while OGTT and serum GPLD1 levels were significantly lower in the T, CFE, and TCFE groups (all p < 0.001). Changes in serum GPC-4 levels were not significant. Serum GPLD1 levels were negatively correlated with insulin levels and HOMA-IS (both p < 0.001).

CONCLUSIONS

This study suggests that endurance training and CFE may downregulate serum GPLD1 levels in STZ-NA-induced diabetic rats, which associate with the serum insulin profile. However, the results show that endurance training and CFE may not cause serum GPC-4 adaptation in STZ-NA-induced diabetic rats.

Heparanase augments insulin receptor signaling in breast carcinoma

Recently, growing interest in the potential link between metabolic disorders (i.e., diabetes, obesity, metabolic syndrome) and breast cancer has mounted, including studies which indicate that diabetic/hyperinsulinemic women have a significantly higher risk of bearing breast tumors that are more aggressive and associated with higher death rates. Insulin signaling is regarded as a major contributor to this phenomenon; much less is known about the role of heparan sulfate-degrading enzyme heparanase in the link between metabolic disorders and cancer.In the present study we analyzed clinical samples of breast carcinoma derived from diabetic/non-diabetic patients, and investigated effects of heparanase on insulin signaling in breast carcinoma cell lines, as well as insulin-driven growth of breast tumor cells.We demonstrate that heparanase activity leads to enhanced insulin signaling and activation of downstream tumor-promoting pathways in breast carcinoma cells. In agreement, heparanase enhances insulin-induced proliferation of breast tumor cells in vitro. Moreover, analyzing clinical data from diabetic breast carcinoma patients, we found that concurrent presence of both diabetic state and heparanase in tumor tissue (as opposed to either condition alone) was associated with more aggressive phenotype of breast tumors in the patient cohort analyzed in our study (two-sided Fisher's exact test; p=0.04). Our findings highlight the emerging role of heparanase in powering effect of hyperinsulinemic state on breast tumorigenesis and imply that heparanase targeting, which is now under intensive development/clinical testing, could be particularly efficient in a growing fraction of breast carcinoma patients suffering from metabolic disorders.

Glypican-3: A promising biomarker for hepatocellular carcinoma diagnosis and treatment

Liver cancer is the second leading cause of cancer-related deaths, and hepatocellular carcinoma (HCC) is the most common type. Therefore, molecular targets are urgently required for the early detection of HCC and the development of novel therapeutic approaches. Glypican-3 (GPC3), an oncofetal proteoglycan anchored to the cell membrane, is normally detected in the fetal liver but not in the healthy adult liver. However, in HCC patients, GPC3 is overexpressed at both the gene and protein levels, and its expression predicts a poor prognosis. Mechanistic studies have revealed that GPC3 functions in HCC progression by binding to molecules such as Wnt signaling proteins and growth factors. Moreover, GPC3 has been used as a target for molecular imaging and therapeutic intervention in HCC. To date, GPC3-targeted magnetic resonance imaging, positron emission tomography, and near-infrared imaging have been investigated for early HCC detection, and various immunotherapeutic protocols targeting GPC3 have been developed, including the use of humanized anti-GPC3 cytotoxic antibodies, treatment with peptide/DNA vaccines, immunotoxin therapies, and genetic therapies. In this review, we summarize the current knowledge regarding the structure, function, and biology of GPC3 with a focus on its clinical potential as a diagnostic molecule and a therapeutic target in HCC immunotherapy.

Inputs and outputs of insulin receptor

The insulin receptor (IR) is an important hub in insulin signaling and its activation is tightly regulated. Upon insulin stimulation, IR is activated through autophosphorylation, and consequently phosphorylates several insulin receptor substrate (IRS) proteins, including IRS1-6, Shc and Gab1. Certain adipokines have also been found to activate IR. On the contrary, PTP, Grb and SOCS proteins, which are responsible for the negative regulation of IR, are characterized as IR inhibitors. Additionally, many other proteins have been identified as IR substrates and participate in the insulin signaling pathway. To provide a more comprehensive understanding of the signals mediated through IR, we reviewed the upstream and downstream signal molecules of IR, summarized the positive and negative modulators of IR, and discussed the IR substrates and interacting adaptor proteins. We propose that the molecular events associated with IR should be integrated to obtain a better understanding of the insulin signaling pathway and diabetes.

The role of hepatokines in metabolism

The liver is known to be involved in the natural history of the ongoing epidemics of type 2 diabetes mellitus and cardiovascular disease. In particular, the liver has a role in increased glucose production and dysregulated lipoprotein metabolism, conditions that are often found in patients with nonalcoholic fatty liver disease. Additionally, several proteins that are exclusively or predominantly secreted from the liver are now known to directly affect glucose and lipid metabolism. In analogy to the functional proteins released from adipose tissue and skeletal muscle-adipokines and myokines-these liver-derived proteins are known as hepatokines. The first hepatokine that has been proven to have a major pathogenetic role in metabolic diseases is α2-HS-glycoprotein (fetuin-A). Production of this glycoprotein is increased in steatotic and inflamed liver, but not in expanded and dysregulated adipose tissue. Thus, research into this molecule and other hepatokines is expected to aid in differentiating between the contribution of liver and those of skeletal muscle and adipose tissue, to the pathogenesis of type 2 diabetes mellitus and cardiovascular disease.